I. Field of the Invention
This invention relates generally to materials handling apparatus, and more particularly to a machine for either stacking or unstacking articles such as wooden pallets and the like.
II. Discussion of the Prior Art
Machinery exists for automating the manufacture of wooden pallets on which products are placed when shipping by truck or rail. In this regard, reference is made to my co-pending application Ser. No. 08/695,936, filed Aug. 12, 1996, which describes a machine for facilitating the assembly and nailing of lumber items when fabricating pallets. Machines are also known for taking the finished pallets from a conveyor and thereafter arranging a plurality of such pallets in a vertical stack. Here, reference is made to the Model 505 pallet stacking machine manufactured by applicant's assignee. In this machine, new pallets are added to the stack by elevating an entire stack and inserting the next pallet at the bottom of the stack and then again elevating the stack preparatory to receiving the next pallet to be added.
Stated otherwise, a new pallet to be added to the stack enters below the stack being built and it is raised to the bottom of the stack. Once the height of the stack reaches a predetermined number of pallets, it must be removed from the stacking machine. To accomplish this, it is necessary to include as a part of the machine a set of outfeed rollers for holding the finished stack at a location that is displaced from the stacking machine so that a new stack can be started. The completed stack now on the outfeed rollers now must be removed therefrom and lowered to the floor, requiring a fork truck and an operator.
Not only does inclusion of the outfeed rollers and the need for a forklift and driver necessarily raise the cost of production of pallets but also, because the lifting mechanism employed must be sufficiently robust to lift an entire stack which may easily weight 1200 lbs., the pneumatic or hydraulic system employed necessarily has to be sufficiently large to handle the load, which too adds to the cost.
Another problem that often arises when prior art pallet stacking machines are used occurs if an irregularly shaped pallet enters the stack. If an uneven pallet is added to the bottom of the stack, it can tip the entire stack that is placed on it. This may require the operator to summon a forklift operator to lift the portion of the stack above the irregular pallet so that the irregular one can be removed from the bottom of the stack.
The present invention obviates all of the foregoing problems by providing a pallet stacking machine that enters a new pallet to a stack by adding it to the top thereof rather than lifting the stack and inserting the new pallet below the others. By using this approach, a stack can be built directly on the ground, which allows an inexpensive pallet jack instead of a forklift to move a completed stack of pallets away from the stacking machine so that a new stack can be created.
It should also be apparent that a pallet stacking machine which adds the newest pallet to the top of the stack only requires the lifting of one pallet at a time. Accordingly, the cost of lifting mechanism and the power supply, whether pneumatic or hydraulic, is reduced. These features necessarily reduce the overall cost of pallet production.